<html>
<head>
<meta charset="UTF-8">
<script type="text/javascript">
var xmlhttp;
function loadXMLDoc(url,callback)
{
	if (window.XMLHttpRequest)
	{// code for IE7+, Firefox, Chrome, Opera, Safari
	  	xmlhttp=new XMLHttpRequest();
	}
	else
	{// code for IE6, IE5
	  	xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
	}
	xmlhttp.onreadystatechange=callback;
	xmlhttp.open("GET",url,true);
	xmlhttp.send();
}
function myFunction()
{
	loadXMLDoc("test.txt",function()
	{
	  if (xmlhttp.readyState==4 && xmlhttp.status==200)
	    {
	    	document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
	    }
	});
}
</script>
</head>
<body>

<div id="myDiv"><h2>单击按钮改变值</h2></div>
<button type="button" onclick="myFunction()">通过 AJAX 改变内容</button>

</body>
</html>